NEW YORK — Mike O’Connor held so much in his left hand. It was the eighth inning tonight, two men were out, one man was on and the Mets led the Phillies by a run. They had entrusted O’Connor with the task that has made a career as a professional pitcher possible for him.

He needed to get a left-handed batter out.

Already he had allowed the potential tying run to steal second. Up two strikes on Philadelphia’s Chase Utley, O’Connor fiddled with the seams of the baseball. He wanted a strikeout, he would say in the aftermath of a disastrous 5-2 defeat that began right here, in this moment. The manager opted for a curveball.

“If I knew that he was going to hang it,” said Terry Collins, shrugging his shoulders like a man who has trusted his bullpen and was punished for that faith, “I wouldn’t have had him throw it in that situation.”

A belt-high curveball ruined everything. For the Mets on this night, their second consecutive game wrecked by a bullpen collapse, one pitch sparked the fire. As Jimmy Rollins raced home, erasing Mike Pelfrey’s bid for a victory, a crowd of 29,337 fans at Citi Field mourned all that had been wasted.

Commence the breakdown. Jason Isringhausen let Utley steal second and an errant throw by catcher Ronny Paulino let him go to third. The next reliever, lefty specialist Tim Byrdak, fell behind another left-handed hitter, Ryan Howard, and hung a slider.

“It was just one of those pitches,” Byrdak said, as if the result was elementary.

Howard hit a two-run double and the Mets (23-28) were soon losers again, for the sixth time in seven games. They refused to capitalize on one of Pelfrey’s best outings this season, a 7 2/3-inning, 116-pitch clinic on amassing ground balls.

Unlike his last start, when a stellar outing against the Yankees imploded in 10 pitches, Pelfrey overcame the makings of a mid-game blowup. He utilized his splitter to complement a mix of four-seam and two-seam fastballs. The Phillies put only six men on base against him.

Yet his offense did him few favors. Shortstop Jose Reyes scored the team’s only two runs. After he raced home on an RBI single by Jason Bay in the third, Philadelphia’s Cole Hamels (7-2) handcuffed them.

“Guys are going to start swinging the bat,” said Pelfrey, who in two starts against Philadelphia this season had allowed 11 runs and collected 18 outs. He can only hope.

In the fourth, the Phillies created a quagmire. After an RBI double by outfielder Raul Ibanez, Pelfrey displayed the jitters of old. He walked catcher Carlos Ruiz. With two men on, his hand failed to grasp the ball properly as he rose to throw. The ball rolled out of his glove. The home-plate umpire, Scott Barry, called a balk.

Luck intervened. Pelfrey hung a splitter to rookie Domonic Brown, who chopped the ball toward Reyes for the inning’s final out.

By the eighth, his tank appeared empty. With two out, Rollins rocked a single up the middle, and Collins tapped his left arm. He opted for O’Connor because Byrdak had already faced Philadelphia’s left-handed batters often this year.

Pelfrey handed the baseball to O’Connor. He stands 6-3. He weighs 185 pounds. He is here for one reason.

Utley did not oblige.

“To go out there and throw four pitches and let the game get away stinks for everybody,” O’Connor (0-1) said. “If I could get that pitch back, I would.”